3:2 Aspect Ratio on the OM-D

I am a Nikon user and enjoy the 3:2 aspect ratio but I was considering purchasing the OM-D. How are 3:2 images produced on a 4:3 sensor? I know some Panasonic models have a sensor slightly larger than is used to produce the final image, to allow 4:3 or 3:2 aspect ratios with no cropping required.

My specific concern is that, if I choose to shoot in 3:2, the OM-D will crop to achieve this aspect ratio. My first lens purchase would be the 9-18 and I'd like to make use of every last mm at the wide end: if cropping is required to achieve a 3:2 aspect ratio, the 9mm wide angle would be more like 10-11mm in practice.